1. Field of the Invention
The present invention relates to a drying end for a machine for the manufacture of fiber webs, for instance paper webs, having a plurality of heatable drying cylinders. The drying end is divided into a plurality of drying-cylinder groups ("drying groups"). Each of these drying groups has an endless support belt of its own which travels, together with the web to be dried, over the drying cylinders and guide rollers. In this connection, the fiber web comes into direct contact with the cylinders while the support belt comes into direct contact with the guide rollers.
The invention relates more particularly to a drying end in which, at least in a substantial proportion of the drying groups, the drying cylinders are arranged in a row which is at least approximately vertical.
2. Background Art
A relevant drying end is known from U.S. Pat. No. 3,868,780. In FIG. 9 of that U.S. patent, each drying group consists of only a single row of cylinders, and each group of cylinders has an endless support belt of its own. In other figures of that U.S. patent, however, so-called double-row drying groups are also shown. For example, FIG. 2 shows a double-row drying group with drying cylinders arranged vertically one above the other. In this drying group, the fiber web to be dried first travels downward through the first row of cylinders and then upward through the second row of cylinders. Naturally, in all cases, only one of the two sides of the web can come into contact with the drying cylinders in such a double-row drying group.
In FIG. 5 and 7, one such double-row drying group is followed by a second double-row drying group. In the second drying group, the web passes first in an upward direction through the first row of cylinders and then in a downward direction through the second row of cylinders. In this way, the other side of the web comes into contact with the drying cylinders in the second drying group so that overall uniform drying on both sides of the web can be obtained. The arrangements in FIGS. 5 and 7 (as well as in FIG. 8) have, however, the disadvantage that the two double-row drying groups are arranged with one shifted vertically with respect to the other.
This disadvantage is avoided in the aforementioned FIG. 9 of U.S. Pat. No. 3,868,780. In that case, the following is provided: In the first drying group, which has only a single row of cylinders, the fiber web travels downward over the drying cylinders, one side of the web contacting the drying cylinders. In a subsequent second drying group, which also has only a single row of cylinders, the fiber web passes upward over the drying cylinders, whereby the other side of the web contacts the drying cylinders. Thus the two sides of the web are alternately guided over the cylinders of, in each case, one row of cylinders, and this process is continued several times in the arrangement in FIG. 9.
One disadvantage of this arrangement is that in the first drying group, the side of the web which was previously the upper side comes into contact with the drying cylinders and, for this reason, the guide rollers which feed the web of paper directly to the following drying cylinders lie on the side of the drying cylinders which is remote from the press end. This is unfavorable because, in the event that the paper web tears, the broke drops down onto a subsequent portion of the support belt rather than directly onto the basement floor. These problems should be avoided, particularly in the first row of cylinders, since broke is produced much more frequently in the first drying group than in the following drying group.
A further disadvantage is that each drying group has only a single row of cylinders. For this reason, there must be a relatively large number of drying groups, support belts, tensioning rollers and adjustment rollers.